There has been considerable interest in recent years in developing high energy density batteries using lithium as a negative electrode. Lithium metal is particularly attractive as an anode active material of an electrochemical battery because of light weight and high energy density of the metal, for example, compared to a lithium-intercalated carbon negative electrode, which increases the weight and volume of the negative electrode to reduce the energy density of a battery due to the presence of non-electroactive materials, and other electrochemical systems having nickel or cadmium electrodes. A negative electrode principally including a lithium metal negative electrode or a lithium metal provides an opportunity to produce a battery which is lighter in weight and has a higher energy density than batteries such as lithium-ion, nickel metal hydride or nickel-cadmium batteries. These characteristics are highly desirable for batteries for portable electronic devices, such as mobile phones and lap-top computers, which are paid with low weighted value in terms of premium.
These types of cathode active materials for a lithium battery are publicly known, and include a sulfur-containing cathode active material including sulfur-sulfur bonds, in which high energy capacity and rechargeability are achieved from the electrochemical cleavage (reduction) and reformation (oxidation) of the sulfur-sulfur bonds.
Lithium-sulfur batteries in which an alkali metal such as lithium is used as an anode active material and sulfur is used as a cathode active material as described above have a theoretical energy density of 2,800 Wh/kg (1,675 mAh), which is much higher than those of other battery systems, and have recently been in the spotlight used for portable electronic devices due to an advantage in that sulfur is abundant as a natural resource, inexpensive, and environmentally-friendly.
However, since sulfur used as a cathode active material of a lithium-sulfur battery is a non-current collector, there are problems in that it is difficult for electrons produced by an electrochemical reaction to move, sulfur leaks into the electrolyte during the oxidation-reduction reaction so that the service life of a battery deteriorates, and furthermore, when an appropriate electrolytic solution is not selected, lithium polysulfide which is a reduced material of sulfur is eluted so that lithium polysulfide may no longer participate in the electrochemical reaction.
Thus, in order to minimize the amount of lithium polysulfide which is dissolved into the electrolytic solution and impart electric conductivity characteristics to a sulfur electrode which is a non-current collector, a technology in which a composite of carbon and sulfur is used as a positive electrode has been developed, but an elution problem of lithium polysulfide still cannot be solved.
Therefore, there is a high need for a technology to enhance cycle characteristics by effectively blocking lithium polysulfide from leaking into the electrolyte during the discharge of a lithium-sulfur battery.